The present invention relates to a vibration attenuator for attenuating the vibration caused during the machining or resurfacing of a disc brake rotor by a pair of cutter bits.
After a period of use the faces of disc brake rotors of automobiles, trucks and the like become worn unevenly. A characteristic pattern of circumferentially arranged ridges and valleys develops which interferes with optimum braking action. Additionally the rotors may become warped which could also have an adverse effect on the vehicle's braking capability as well as the undesirable effect of transmitting a pulsing to the brake pedal. The grooves and/or warpage must be removed by resurfacing or machining the face of the rotor. Typically, this is done by mounting the rotor on an arbor assembly for rotation by a brake rotor lathe. A pair of cutter bits are moved by the lathe carriage across the faces of the rotating rotor to cut enough of the material away to render the faces flat or planar. During this operation the cutter bits and rotor typically produce loud, screeching noises which are not only unpleasant for the lathe operator and others in the vicinity, but the accompanying vibrations of the rotor and bits can adversely affect the accuracy of the machining. The vibration may also have an adverse effect on the bits causing them to over heat and wear prematurely.
Various means have been advanced to attenuate or eliminate such vibrations. One system employs damping pads designed to bear against the opposite faces of the rotor in a position out of the way of the cutter bits. The pads are carried by a relatively complex mounting structure which is secured to the brake lathe. Precise adjustment of the position of the pads is required, and an elaborate linkage arrangement is provided to accomplish this. The arrangement is relatively complex and costly, requires subtle adjustments, and is only partially effective in damping the machining noises.
Another system of the prior art utilizes a resilient band adapted to be stretched and placed about the circumference of the rotor. One must purchase a set of such bands to accommodate each of the various sizes of rotor to be machined. The system is unsatisfactory for that reason, and also because the vibration attenuation is not always adequate.
Yet another arrangement of the prior art employs a U-shape rod or handle which mounts a pair of friction resistant pads at its extremities. The pads are placed in position to bear against the opposite faces of the rotor to thereby damp rotor vibration. However, the pads are not effective to attenuate cutter bit vibrations.
U.S. Pat. No. 4,531,434 describes a device wherein two friction pads are biased against the rotor surfaces while the rotation of the rotors then forces the pads against the cutter arms and bits. Pins projecting from the pads engage the cutter arms to automatically maintain the pads in radial position relative to the arms or bits as they are gradually drawn across the faces of the rotor. However, its use in many lathe configurations is compromised in that the cutter bits must be extended an inordinate distance from the cutter arms in order to provide direct access to the bits by the pads. Although the resulting direct contact of the bit enhances the attenuating effect, the extension of the bit substantially offsets such effect as significantly greater vibration is being generated. Additionally, the handle of the device described in the patent interferes with the lathe carriage of many lathe systems which forces the pads to be angled relative to the bits and therefore further diminishes their efficacy. Further, in certain brake rotor lathe configurations, the cutter bit is attached to the cutter arm by a fastener that interferes with the direct contact of the bits by the attenuator pads as the pads are driven towards the bits by the rotation of the rotor. While such attenuator mechanism is fairly effective in attenuating the vibration, further improvement is desirable.